My tuned A10 has 9:1 pistons, a Spitfire cam and a gas flowed head with new valve seats fitted (old ones were quite recessed)
It pinks really badly on std 95 unleaded fuel and borders on the unusable. I run it on 98 Octane Shell V-power and it's transformed - running really well with minimal pinking. On V-power, if it does start pinking, a large handful of throttle stops it. I tried Tesco's Momentum 97 Octane fuel and it's OK, but significantly worse than Shell V-power. If there is no Shell garage nearby, it's a decent backup.
I have run it on AVgas (fully leaded aviation fuel) , and the pinking completely disappears.
Use the highest octane fuel that you can on any A10 with a high compression ratio and you'll see a massive difference. On 7:1 pistons on a basic Flash engine, std 95 octane fuel is fine.
okay, I would agree with most of that, but again it REALLY makes a difference about region and location And I cant offer any opinions on what currently comes out of the pump in the UK or Australia, but here in the US what is pumped in Los Angeles Calif is totally different than what is pumped in Denver Colorado.
It may say the same ratings on the pump but its formulated differently, as well as Summer, fall, winter and Spring blends.. Theres countless articles on how that works. In my area, most of our petrol is brewed up near the Canadian border and they make a base stock, and then add chemicals to suit, But California has its own refinerys and what they blend up is totally different.
Octane ratings are a complicated topic and the chemistry is quite complex, When I was racing we spent a lot of time learning how these fuels work and what was brewed back in the 1960s is totally different than now. In the military as well as Aerospace applications whether is jet fuel or recip acft fuel stds are constantly tested and evaluated. What the consumer is being sold is barely regulated or tested and the incentives to cheat is quite high. A tidy profit can be made by adulterating fuel and most people would never notice.
But the long and short of it is that for compression, an engine only needs just enough octane. Adding more does not add power. If you were getting substd fuel to begin with a better grade might seem a revelation but running something like AVGAS in a old motorcycle can create a lot of problems. Plug fouling to start, But its blended for totally differnt conditions.
In a old BSA in Blighy lets say chances are you are 250 to 400 feet above sea level, Summer temps or even winter at Ambient temps are going to be in the range of 45 to 65 deg F, Inlet temps past the carb flange will be quite high, probably around 80 to 100 deg F on a cast iron and less in a Alloy head as there is a cooling process thru contraction and expansion.
Now a recip acft at 8,000 foot with temps at or below freezing, Carb or inlet icing is a significant problem so many acft have to heat the fuel just to prevent problems and carbs or injectors often have warming devices as Ice going into an intake is just as bad as a stray wrench. So the fuel is formulated to temp and altitude.
A fuel designed to operate in a stable manner well below freezing is not going to be very manageable outside that parameter. An early Cheat that Smokey did was to chill the fuel before a race to near freezing as it becomes much more dense, Avgas is formulated for that, Street gas is not.
Not much fully leaded avgas anymore, Its typically 100LL which is low lead. This is the ratings and types of AVGAS sold in the US. In some areas regular 100 is sold but its a regional thing. In my area most FSBO sell LL.
Grade Color Lead / Gallon
80/87 Red 0.5 mL
100LL Blue 1.2 - 2.0 mL
100/130 Green 3.0 - 4.0 mL
115/145 Purple 4.6 mL
Here is one of many out there that explains the difference between Automotive fuels and Aviation fuels
(Big differences and not just price)
See:
http://www.aviationpros.com/article/10387611/octane-101-autogas-vs-avgasOctane 101
The octane rating of gasoline refers to the fuel's anti-knock quality, Autogas octane is rated differently than that of avgas. Two CFR (Cooperative Fuel Research) knock-test engines, adopted by ASTM, are used to test automotive gasoline according to ASTM D 2699 and D2700 standards. A modified version of the CFR engine is used to test avgas. The ASTM D 2699 test refers to the Research Octane Method (RON) and serves as the essential index of acceleration knock. ASTM D 2700 refers to the Motor Octane Number (MON) and provides an index of knock at high engine speeds. The (MON) method engine test differs from the (RON) method by using preheated fuel mixtures, higher engine speeds and variable ignition timing, placing more stringent thermal demands on the fuel under test. The (MON) number is typically 8 to 10 octane numbers lower than the (RON) number.
The autogas (MON) octane number is similar to the aviation rating of octane up to 100 octane, according to ASTM D 2700. When you purchase autogas, the octane rating is the average of the RON and MON, (R+M)/2 and the formula is posted on the gasoline dispenser. However, you have no way of knowing if the (MON) octane number meets the requirements of your aircraft engine unless you have documentation or a means to test gasoline octane on-site.
-------------------------------------More at that site or many others.,
Smokey Yunick, famed engine builder and tuner wrote extensively on fuel sciences and he was a genius. For anyone who wants a better understanding of anything related to engine performance any of his books are a must have. For years he wrote monthly columns in Circle track racing magazine and I subscribed for years just to read Smokeys articles alone.
see:
http://www.hotrod.com/articles/ctrp-0801-smokey-yunick/But to understand fuels in an engine like the BSA you have to understand that a liquid fuel is useless. It wont burn. It has to be vaporized and the better the vaporization the more efficient it is. This is why HOW the fuel atomizes into a vapor is critical and WHY the formulation of the fuel is also critical. To do that you have to understand how the Reid Vapor curve works and is measured. Big inch motors with fat cams, big valves and ports are horrible at this (IE: Harleys) But early BSAs had very inefficient intakes, valves and valve angles and a crude carb to boot. They key is to figure out HOW to get fuels to convert from liquid form to a vaporized mist and the chemistry of the fuel itself is most of the equation. Then the key is how to light it efficiently so,,many of us have limited choices for fuels so you should look at optimizing the ignition which is why the stock maggies have a severe deficit. In other words on a 1950s BSA you have very limited options.
But to get a better understanding of HOW efficient a OHV IC can be, read this or others on this topic..
see:
http://www.rexresearch.com/yunick/yunick.htm" Smokey calls it his “Phase I adiabatic engine”. Adiabatic is an engineering term that refers to any process in which there’s no gain nor loss of heat.
A completely adiabatic engine isn’t possible, but the closer you get, the higher the engine’s efficiency and the better the fuel mileage. In other words, the less heat energy generated by the burning fuel that you throw away through the exhaust and cooling systems (much like the vehicles we all drive today), the more energy there’s available to move the car."
-And-
" Smokey describes his tests with fuel vaporization: “On the flow bench and on the dynamometer, we’d pull out a sample of air-fuel mixture mixed by the standard carburetor, and you couldn’t punch a stopwatch fast enough before the mixture started to separate into a liquid and air again. But, when the mixture goes through the entire heated process and then through the homogenizer, it’s 20 minutes before it starts to settle out”."
So that should suffice to get you guys interested in fuels, But if we were all smart we would be running these vehicles on Natural gas or propane, It burns totally clean, almost no emissions, oil fouling,. little wear
and economical but thats another topic.
